PROJECT SUMMARY/ABSTRACT One of the current challenges in restoring vision through regeneration of the retina is the lack of means to activate endogenous progenitor cells for the production of a sufficient number of functional photoreceptors, as reflected in the NEI Audacious Goal Initiatives ( . To undertake this challenge, this project investigates a rather unconventional approach to photoreceptor regeneration ? tapping into the regenerative potential of a nearby tissue, the retinal pigment epithelium (RPE), for photoreceptor regeneration in the mouse eye using gene-directed reprogramming. Our long-term goal is to elicit photoreceptor regeneration in the mammalian eye for replacement without cell transplantation. NOT-EY-14-003) Recent studies using mammalian RPE cell cultures and transgenic mice have produced evidence for the feasibility of this unconventional approach to photoreceptor regeneration in the eye. Moving forward, this project tests the hypothesis that mammalian RPE's regenerative potential, when unlocked by proneural gene neurogenin3 (or neurogenin1), can produce functional photoreceptors and new RPE cells to sustain RPE structure and function. Experiments are designed to achieve two specific aims. Specific Aim 1 determines whether an RPE cell, when primed by neurogenin3, directly undergoes RPE-to-photoreceptor transformation (i.e., transdifferentiation), or if it first goes through a transformation into a progenitor-like stage generating cells with the potentials to differentiate into photoreceptor cells and RPE cells. This study promises to shed light on the cellular mechanisms of how the RPE gives rise to photoreceptor cells and replenishes itself. Specific Aim 2 determines whether functional photoreceptors can be generated in adult mouse using a gene delivery approach compatible with human application, and whether the RPE will be preserved structurally and functionally. This study is expected to produce compelling evidence supporting human feasibility of engaging the RPE as a convenient source of new photoreceptors for functional repair in situ without involving cell transplantation and the associated risks and potential complications.